CN115698512A

CN115698512A - Centrifugal pump for conveying media containing solids

Info

Publication number: CN115698512A
Application number: CN202180044889.1A
Authority: CN
Inventors: M·匹特罗夫
Original assignee: KSB SE and Co KGaA
Current assignee: KSB SE and Co KGaA
Priority date: 2020-06-26
Filing date: 2021-06-23
Publication date: 2023-02-03
Also published as: EP4172505A1; WO2021260000A1; US20230258187A1; DE102020003855A1

Abstract

The invention relates to a centrifugal pump for conveying a medium containing solids. The centrifugal pump has at least one component (13,20,25) for reducing backflow from the first space into the second space. The assembly (13,20,25) includes at least one non-rotating element (2,6,21) that cooperates with at least one rotating counter-element (14,22). The element (2,6,21) has at least in part a layer of carbon.

Description

Centrifugal pump for conveying media containing solids

Technical Field

The invention relates to a centrifugal pump for conveying a medium containing solids, comprising a component for reducing the backflow from a first space into a second space.

Background

Centrifugal pumps have gaps through which flow can pass at different points, such as for example between the impeller and the housing, where the pressure difference causes leakage flows which are partly very lost. The seal must be selected in such a way in relation to the order of magnitude of the gap that it is not too large, so that the efficiency of the centrifugal pump is reduced by high losses via this gap, but the gap is not allowed to be too small, since otherwise there is the risk of collisions (Anlaufen), i.e. contact between rotating and stationary components, occurring.

Such a seal may be, for example, a clearance ring seal assembly. The gap ring seal is used in centrifugal pumps to seal spaces of different pressures. The assembly includes a non-rotating element and a rotating element. The non-rotating element can be, for example, a clearance ring, which is arranged at the housing, either the housing itself or the housing part. The rotating element may for example be a bearing ring (sometimes called a race ring) arranged on the impeller, or the impeller itself or a part of the impeller, e.g. a cover disc of the impeller in closing the impeller.

The gap formed between the rotating and non-rotating elements acts as a throttle between the spaces of different pressures and prevents an excessively high flow from the space of higher pressure into the space of lower pressure. The smaller the gap between the two elements, the higher the efficiency loss of the centrifugal pump. However, this effort is hampered by the fact that too little clearance is very difficult to conform to manufacturing tolerances and operational effects. It is useful to avoid contact between the elements in order to prevent the rotating elements from rubbing over the non-rotating elements and thus to prevent wear. Due to the tolerances necessary in the production of the individual components, there is a minimum clearance range which prevents the elements from being touched and thus from rubbing and wearing. However, during operation, in particular when the pump is started or started, situations have arisen in which contact occurs and then pressing or material wear occurs.

In the transport of solids-containing media, the widening of the gap caused by the erosive action of the contaminated components must also be taken into account. The increased efficiency losses are therefore considered above all in the case of a centrifugal pump for contaminated water.

Exemplary of solids-containing media are waste waters, in particular municipal and industrial waste waters. It typically includes pipe waste water (e.g., sewage, manure), waste water (mechanically cleaned water from sewage purification tanks), sludge (e.g., activated sludge, fresh sludge, digested sludge, and inoculated sludge), and rain water. Industrial waste water can act very aggressively or aggressively on the components of the centrifugal pump used, in particular the medium-contacting components of the centrifugal pump.

In order to take into account the constant wear of the gap seal at the centrifugal pump for conveying aggressive fluids, it has already been proposed to provide the adjustment possibility of the gap via an adjustable sealing element. DE 35 13 A1 describes such a gap seal. Such manually adjustable clearance seals are relatively expensive to manufacture and require substantial experience from operating professionals. The adjustment, control and time calibration of the sealing element requires a proportionally higher effort.

Generally, cast iron components are often used in centrifugal pumps. During casting, a solid material in the desired shape emerges from the liquid material after hardening. In this way, the desired housing structure or the remaining components of the impeller or centrifugal pump can be produced in a targeted manner. The cast iron material in centrifugal pump construction is typically an iron carbon alloy.

DE 10 2017 223 602 A1 describes a pair of clearance ring carrying rings of a centrifugal pump based on silicon carbide. The hardness of the material should protect the centrifugal pump from erosive wear. For this purpose, ceramic elements made of silicon carbide are inserted into a cast iron material and subsequently cast with a metallic cast iron material.

DE 10 2018 214 650 A1 describes a gap ring seal for centrifugal pumps based on aragonite-modified calcium carbonate, which has wear resistance with respect to aggressive materials with a high hardness.

In particular in centrifugal pumps for conveying media containing solids, signs of corrosion or wear occur in the region of the gap ring seal. Due to the high fragility of the ceramic materials, which are resistant to corrosion in most cases, the proposed ceramic solutions are often very expensive and costly to implement in certain component geometries and can possibly lead to operational disturbances (for example by breaking off of components).

Disclosure of Invention

The object of the invention is to provide a centrifugal pump for conveying a medium containing solids. The damage of the clearance ring by erosion wear should be effectively reduced. Furthermore, the pump should be able to maintain efficiency for a long time during operation. Centrifugal pumps should be distinguished by high reliability and long service life. It should furthermore ensure a simple assembly. Furthermore, centrifugal pumps should be convincing by manufacturing costs that are as low as possible.

This object is achieved according to the invention by a centrifugal pump for conveying a medium containing solids having the features of claim 1. Preferred variants can be gathered from the dependent claims, the description and the drawings.

According to the invention, a centrifugal pump for conveying a medium containing solids with at least one component for reducing back flow has a non-rotating element which has at least partially a layer made of carbon.

Such an assembly for reducing backflow can be designed according to the invention as a gap seal, which can be formed by a gap ring and a carrier ring or by a gap ring and an impeller. The assembly is used to seal spaces of different pressures and acts as a throttle between these spaces. In this assembly, the first space is understood to be the space with the higher pressure and the second space is understood to be the space with the lower pressure. In centrifugal pumps, the correspondingly higher pressure space is the space of the pressure connection and the screw housing. The lower pressure space is the space of the suction area in front of the impeller.

The spacer ring is arranged by means of a press fit at the pump housing and is fixed and non-rotating correspondingly thereto. The gap ring is thus arranged directly at the pump housing. Furthermore, it forms a gap with the rotating counter-element. The rotating element can be, for example, a carrier ring, which is arranged on the impeller, or the impeller itself or a part of the impeller, for example, in the closed impeller, the radial and/or axial face of a cover disk of the impeller.

Advantageously, the gap ring has a carbon layer at a radial face, such as for example at the inner side of the gap ring, and/or at an axial face, such as for example at the end side of the gap ring. As a result, the hardness of the normal gap ring made of a cast iron material and/or a stainless steel material is greatly increased. The gap ring thus obtains effective protection against the erosive action of solid particles in the conveying medium.

Particularly advantageously, the carbon layer is in respect of a touch or impact of the counter element. Due to the particularly flat surface of the carbon layer and its particular hardness, the gap ring appears to be insensitive to the wiping action of the mating element.

In a variant of the invention, a second clearance ring for sealing the impeller against the bearing-carrying cover is used. Likewise, the intermediate ring has a carbon layer which protects the intermediate ring, in particular with respect to the erosive action of the solids-containing medium and the undesired contact of the impeller.

According to the invention, the play ring interacts with the counter element in order to prevent particularly small play for reducing a backflow from the higher-pressure space of the pump into the lower-pressure space. The counter element can be designed in the form of a carrier ring which is arranged on a prepared face of the cover disk of the impeller. In an alternative variant, the mating element can be configured in the form of a machined radial and/or axial surface of the cover disk of the impeller. In both variants, according to the invention, a carbon layer is applied to the surfaces forming the gaps. Ideally, the rotating counter element is thereby protected from the erosive effects of the solid-containing medium.

Particularly advantageous is the design of the spacer ring made of a conventional metal material, in particular a cast iron material and/or a stainless steel material, which is subsequently coated with a particularly hard and corrosion-protected carbon layer. In this way, the spacer ring can be produced from cost-effective raw materials, which at the same time can be processed in known standard production methods.

A carbon layer is understood to be a layer in which carbon is the main constituent. The carbon layer can be applied, for example, in a PVD (Physical Vapor Deposition) Physical Vapor Deposition, for example by evaporation or sputtering, or in a CVD (Chemical Vapor Deposition) method.

Preferably, it is an amorphous carbon layer, in particular a tetrahedral, hydrogen free amorphous carbon layer, also referred to as ta-C layer. The atomic bonds belonging to the crystal lattice of graphite (3 respectively in general) are labeled with the designation "sp 2". Here, sp2 hybridization is present.

In the diamond layer, each carbon atom with four adjacent atoms forms a tetrahedral arrangement. In this spatial arrangement, all atomic spacings are equally small. It therefore acts with very high bonding forces between the atoms, and more precisely in all spatial directions. Thereby producing the high strength and extreme hardness of diamond. The atomic bonds belonging to the crystal lattice of diamond, four in general, are labeled with the designation "sp 3". Thus, sp3 hybridization occurs.

In a particularly suitable variant of the invention, the carbon layer consists of a mixture of sp3 and sp 2-hybridized carbon. The layer is marked by an amorphous structure. External atoms, such as hydrogen, silicon, tungsten or fluorine, may also be incorporated into the carbon network.

The arrangement according to the invention of the carbon layer on the gap ring and the counter element, such as for example the carrier ring, leads to a significant reduction in the erosive wear.

By the arrangement of the carbon layer on the spacer ring, an extremely smooth axial surface with anti-adhesive properties is created without costly mechanical reworking of the impeller. Furthermore, a plurality of clearance rings can be brought in a coating reactor, which is preferably embodied as a vacuum chamber, wherein the ta-C coating is applied in a large thermal load. The centrifugal pump according to the invention with at least one clearance ring is therefore distinguished by a comparatively low production cost.

In a particularly advantageous variant of the invention, the carbon layer is applied as a coating to the spacer ring. The thickness of the layer is advantageously more than 0.5 micrometer, preferably more than 1.0 micrometer, in particular more than 1.5 micrometer. Furthermore, it has proven to be suitable for the carbon layer to be less than 18 micrometers, preferably less than 16 micrometers, in particular less than 14 micrometers.

Ideally, the coating consisting of carbon has an extremely smooth axial surface with anti-adhesive properties, in which the central roughness value R of the carbon layer _a Is less than 0.7 micrometer, preferably less than 0.5 micrometer, especially less than 0.3 micrometer.

the ta-C coating has a very low coefficient of friction at the same time as very good chemical resistance. The hardness of the coating is very close to that of diamond, wherein the hardness is preferably more than 20GPa, preferably more than 30GPa, especially more than 40GPa and less than 120GPa, preferably less than 110GPa, especially less than 100GPa.

The ta-C coating is harder than the a-C: H layer by an average of 40 to 75GPa. Furthermore ta-C contains no hydrogen. Thus, it is assumed that ta-C: H is more resistant to contact with water than ta-C (at temperatures above 80 ℃). In contact with other, especially polar liquids containing molecules in which hydrogen is attached, ta-C may likewise be more resistant than a-C: H.

Preferably, the carbon layer is not applied directly to the gap ring, but it is first provided with an adhesion relay layer. It is preferably composed of a material which not only adheres well to the steel but also prevents carbon diffusion, for example by forming more stable carbides. As an adhesion relay layer satisfying these requirements, a thin layer suitably composed of chromium, titanium, or silicon is used. In particular, chromium carbide and tungsten carbide have proven to be adhesion relays.

In an advantageous variant of the invention, the coating has an adhesion relay layer, which preferably contains a chromium material. Preferably, the adhesion relay layer consists of chromium up to more than 30 weight percent, preferably more than 60 weight percent, in particular more than 90 weight percent.

The ta-C coating according to the invention is a simple, quickly implementable and economical coating for a clearance ring in a centrifugal pump. The coating according to the invention also has outstanding sliding properties and good chemical resistance, in addition to a very high hardness. In particular, most metallic materials are distinguished by a higher ductility directly compared to ceramic materials.

The advantage of the higher hardness of the ta-C coating is that small and large solid particles, which are often contained in solids-containing media, can then act on the gap seal, i.e. the gap ring and the mating element, with a strongly reduced erosion. By flowing, these solid particles normally function as abrasive means. The gap ring, the carrier ring, the impeller and/or the suction-side housing part coated with ta-C have an extremely hard protective layer with respect to corrosion, as a result of which their service life is significantly increased in the transport of solids-containing media.

Preferably, a PECVD/PACVD method is used for the coating. In this case, the plasma excitation of the gas phase takes place by coupling pulsed direct voltage ("pulsed DC"), medium-frequency (KHz range) or high-frequency (MHz range) power. For reasons of the process variability which is maximized in different workpiece geometries and load densities, the coupling of the pulsed direct voltage has furthermore proven to be effective.

Ideally, a PVD method is used for the cladding. The process is particularly simple and has a low process temperature. This technique results in a layer into which external atoms can also be loaded as desired. The process guidance is preferably carried out in such a way that structural and dimensional changes of the material to be coated (metallic gray cast iron, etc.) are excluded.

The ta-C coating has the advantage over CVD diamond layers that the coating temperature is 600 to 1000 ℃ for CVD diamond layers and clearly below 500 ℃ for amorphous carbon layers such as ta-C. This is of high technical relevance in particular for coatings of metallic materials. The manufacture of PVD diamond layers is not possible.

Drawings

Further features and advantages of the invention emerge from the description of the embodiments and from the figures themselves in accordance with the figures.

Wherein:

figure 1 shows a sectional view of a centrifugal pump for conveying solids-containing media with a closed impeller,

figure 2 shows a sectional view of a centrifugal pump for conveying solids-containing media with a closed single-vane wheel,

figure 3 shows a cross-sectional view of a centrifugal pump for conveying solids-containing media with a closed single-channel wheel,

figure 4 shows a partial enlargement in the area of the suction nozzle,

figure 5 shows a detailed cross-sectional view of a fixed non-rotating element.

Detailed Description

Fig. 1 shows a sectional view of a centrifugal pump for conveying a solids-containing medium with two assemblies for reducing

backflow

13,25 from a first space into a second space. The

assembly

13,25 includes two non-rotating elements 2,6 which in this embodiment co-act with the closed impeller 4. This embodiment is a horizontally disposed spiral shell pump. The elements 2 and 6 are designed in this embodiment as clearance rings. Via the suction nozzle 1, the medium containing solids flows into the pump, is acted upon by kinetic energy by the closed impeller 4, which is connected in a rotationally fixed manner with the shaft 9 at the fastening point 12, and leaves the housing part 10, which is embodied in the example as a pump housing, via the pressure connection 5. The shaft 9 is rotatably supported by the ball bearing 8. The housing part 7, which is designed as a pressure cover in this exemplary embodiment, closes the pump space in the direction of the drive. Elements 2 and 6 are ideally coated with a carbon layer, preferably an amorphous carbon layer, in particular ta-C. In this way, a particularly desirable protection against erosive wear is obtained, which necessarily acts on the clearance ring when conveying solids. The ceramic material base, such as silicon carbide, can be omitted due to the flat and extremely hard ta-C coating of the gap ring. The gap ring can be made of a usual cast iron material or a usual stainless steel material and is protected from the erosive action of the solids-containing medium by a ta-C coating.

In the region of the suction nozzle 1, in the interior of the housing part 10, a stationary, non-rotating element 2 (here embodied as a clearance ring) is connected to the housing part 10 by means of a press fit. The element 2 and the impeller 4 are spaced apart from each other so that a gap is formed between the element 2 and the impeller 4, which acts as a sealing gap with geometrically identically configured faces.

Fig. 2 shows a sectional view of a centrifugal pump for conveying a medium containing solids with an assembly for reducing the return flow 13 from the first space into the second space. The assembly 13 comprises a fixed non-rotating element 2 which in this embodiment co-acts with a closed single-bladed wheel 4. The element 2 is configured in this example as a gap ring. Via the intake nozzle 1, the medium containing the solids flows into the pump, is acted upon with kinetic energy by the closed one-blade wheel 4, which is connected in a rotationally fixed manner to the shaft 9, and leaves the housing part 10 via the pressure connection 5. The shaft 9 is rotatably supported by the ball bearing 8. The housing part 7, which is designed as a pressure cover in this exemplary embodiment, closes the pump space in the direction of the drive. According to the invention, the component 2 is coated with a carbon layer, preferably an amorphous carbon layer, in particular ta-C. In this way, a particularly desirable protection against erosive wear is obtained, and also against collision of the closing single-blade wheel against the clearance ring.

Fig. 3 shows a sectional view of a centrifugal pump for conveying a medium containing solids with an assembly for reducing the return flow 13 from the first space into the second space. The assembly 13 comprises a fixed non-rotating element 1 which in this embodiment co-acts with a closed single-bladed wheel 4. The element 2 is constructed in this embodiment as an L-shaped clearance ring, which is coated at the surface with ta-C. Via the suction nozzle 1, the medium containing the solids flows into the pump, is acted upon with kinetic energy by the closed one-blade wheel 4, which is connected in a rotationally fixed manner to the shaft 9, and leaves the housing part 10, which is designed as a pump housing, via the pressure connection 5. The shaft 9 is rotatably supported by the ball bearing 8. The housing part 7, which is designed as a pressure cover in this embodiment, closes the pump space in the direction of the drive. According to the invention, the L-shaped element 2, also called angular gap ring, is coated with a carbon layer, preferably with an amorphous carbon layer, in particular with ta-C. As a result, a particularly desirable protection against erosive wear is obtained and also against collision of the closing single-blade wheel 4 against the clearance ring.

Fig. 4 shows a detail of a variant according to the invention in the region of the suction nozzle 1. The centrifugal pump has an assembly in the form of a clearance seal for reducing the back flow 13. It comprises a rotating member 14, configured as a carrier ring, and a non-rotating member 2, configured as a clearance ring. The rotating member 14 is arranged at the radial outside of the cover disc 3 of the impeller 4. The rotating member 14 thus rotates with the impeller 4. The non-rotating component 2 is arranged at the housing part 10 and has a radial ring inner side as a guide, which co-acts with a radial ring outer side of the rotating component 14, which in the embodiment is configured as an angle-carrying ring and forms a gap seal. The element 2 and the rotation member 14 are according to the invention coated with a carbon layer, preferably an amorphous carbon layer, in particular ta-C. A particularly desirable protection against erosive wear is thereby obtained.

In the embodiment according to the view in fig. 4, in addition to the assembly for reducing backflow 13, a further assembly 20 is provided, which comprises a rotating element 22 and a non-rotating element 21. The rotary element 22 is designed as a ring, which is arranged on the axial end side of the cover disk 3 and is likewise referred to as an angle carrier ring. For this purpose, the rotary element 22 has a projection 19 extending in the axial direction, which engages in the groove 15 of the cover disk 3. The non-rotating element 21 is configured as an axially movable ring which is guided by the face 16 of the housing part 10 with respect to radial movement. The force generating element 17 exerts a force on the non-rotating element 21 and presses the non-rotating element 21 against the rotating element 22. The force generating element 17 is configured as a spring. In an embodiment, a wave spring is used here. In alternative embodiments of the invention, sinusoidal springs or a group spring system (gruppeffederung) may be used. The non-rotating element 21 is sealed by the sealing element 18 to the housing part 10. The sealing element 18 is preferably an O-ring.

The rotating element 22 and the non-rotating element 21 are in the embodiment implemented in stainless steel material, which is according to the invention coated with ta-C. The two axially directed end faces of the rotating element 22 and the non-rotating element 21 are pressed against each other by the force generating element 17. A minimum gap occurs here. Friction is minimized by the ta-C coating. A lubricating film of the transport medium is formed in the gap between the contact surfaces of the rotating element 22 and the non-rotating element 21. The assembly 20, together with the device 13, prevents a back flow from the pressure space 5 of the pump into the suction space 1 of the centrifugal pump.

Fig. 5 shows a detailed cross-sectional view of the non-rotating element 2, which is carbon coated at the axial surface 23 and at the radial surface 24. By means of the ta-C coating on the at least one gap ring end side and on the at least one gap ring inner side, the gap ring can be produced from a conventional cast iron material or stainless steel material and the wear-resistant properties are achieved by means of the ta-C coating.

Claims

1. A centrifugal pump for conveying a medium containing solids, with at least one assembly (13,20,25) for reducing backflow from a first space into a second space, wherein the assembly (13,20,25) comprises at least one non-rotating element (2,6,21) which interacts with at least one rotating counterpart element (14,22),

it is characterized in that the preparation method is characterized in that,

the element (2) has at least partially a layer made of carbon.

2. The centrifugal pump according to claim 1, wherein the non-rotating element (2,6,21) is arranged directly at a housing piece (10,7).

3. A centrifugal pump according to claim 1 or 2, wherein the non-rotating element (2,6,21) is configured as a clearance ring.

4. A centrifugal pump according to any one of claims 1 to 3, wherein the non-rotating element (2,6,21) has a layer of carbon at the radial face (24).

5. A centrifugal pump according to any one of claims 1-4, wherein the non-rotating element (2,6,21) has a layer of carbon at the axial face (23).

6. Centrifugal pump according to any one of claims 1 to 5, wherein the non-rotating elements (2,6,21) co-act with rotating counter-elements (14,22) arranged at the cover disc (3) of the impeller (4) or with axial and/or radial faces of the cover disc (3).

7. The centrifugal pump according to claim 6, wherein the mating element (14,22) is configured as a load ring.

8. A centrifugal pump according to claim 6 or 7, wherein the counter element (14,22) has at least in part a layer of carbon.

9. Centrifugal pump according to one of claims 6 to 8, wherein the closed impeller (4) has a layer of carbon at least in part at the axial and/or radial face of the cover disc (3).

10. The centrifugal pump according to any one of claims 1 to 9, wherein the element (2,6,21) and/or the counter element (14,22) are made of a metallic material, preferably a cast iron material or a stainless steel material.

11. The centrifugal pump according to any one of claims 1 to 10, characterized in that it is an amorphous carbon layer.

12. The centrifugal pump according to any one of claims 1 to 11, which is a tetrahedral hydrogen free amorphous carbon layer.

13. A centrifugal pump according to any one of claims 1 to 12, wherein the thickness of the carbon layer is more than 0.5 microns, preferably more than 1.0 microns, especially more than 1.5 microns, and/or less than 18 microns, preferably less than 16 microns, especially less than 14 microns.

14. A centrifugal pump according to any one of claims 1-13, characterized in that the surface hardness of the carbon-coated surface of the non-rotating element (2,6,21) is more than 20GPa, preferably more than 30GPa, especially more than 40GPa, and/or less than 120GPa, preferably less than 110GPa, especially less than 100GPa.